The present invention relates to the field of chemical mechanical polishing. More particularly, the present invention relates to methods and apparatus for polishing a semiconductor wafer to a high degree of planarity and uniformity. This is achieved when the semiconductor wafer is polished with pads at high bi-directional linear or reciprocating speeds. The present invention is further directed to a wafer housing for loading and unloading wafers.
Chemical mechanical polishing (CMP) of materials for VLSI and ULSI applications has important and broad application in the semiconductor industry. CMP is a semiconductor wafer flattening and polishing process that combines chemical removal of layers such as insulators, metals, and photoresists with mechanical polishing or buffering of a wafer layer surface. CMP is generally used to flatten surfaces during the wafer fabrication process, and is a process that provides global planarization of the wafer surface. For example, during the wafer fabrication process, CMP is often used to flatten/polish the profiles that build up in multilevel metal interconnection schemes. Achieving the desired flatness of the wafer surface must take place without contaminating the desired surface. Also, the CMP process must avoid polishing away portions of the functioning circuit parts.
Conventional systems for the chemical mechanical polishing of semiconductor wafers will now be described. One conventional CMP process requires positioning a wafer on a holder rotating about a first axis and lowered onto a polishing pad rotating in the opposite direction about a second axis. The wafer holder presses the wafer against the polishing pad during the planarization process. A polishing agent or slurry is typically applied to the polishing pad to polish the wafer. In another conventional CMP process, a wafer holder positions and presses a wafer against a belt-shaped polishing pad while the pad is moved continuously in the same linear direction relative to the wafer. The so-called belt-shaped polishing pad is movable in one continuous path during this polishing process. These conventional polishing processes may further include a conditioning station positioned in the path of the polishing pad for conditioning the pad during polishing. Factors that need to be controlled to achieve the desired flatness and planarity include polishing time, pressure between the wafer and pad, speed of rotation, slurry particle size, slurry feed rate, the chemistry of the slurry, and pad material.
Although the CMP processes described above are widely used and accepted in the semiconductor industry, problems remain. For instance, there remains a problem of predicting and controlling the rate and uniformity at which the process will remove materials from the substrate. As a result, CMP is a labor intensive and expensive process because the thickness and uniformity of the layers on the substrate surface must be constantly monitored to prevent overpolishing or inconsistent polishing of the wafer surface.
Accordingly, an inexpensive and more consistent method and apparatus for polishing a semiconductor wafer are needed.
It is an object of the present invention to provide methods and apparatus that polish a semiconductor wafer with uniform planarity.
It is another object of the present invention to provide methods and apparatus that polish a semiconductor wafer with a pad having high bi-directional linear or reciprocating speeds.
It is still another object of the present invention to provide a polishing method and system that provides a xe2x80x9cfreshxe2x80x9d polishing pad to the wafer polishing area, thereby improving polishing efficiency and yield.
It is still a further object of the present invention to provide a drive system for providing the fresh polishing pad from a roll of a polishing pad such that the lifetime of the polishing pad is maximized.
These and other objects of the present invention, among others, either singly or in combination, are obtained by providing methods and apparatus that polish a wafer with a pad having high bi-directional linear speeds. The present invention includes a polishing pad or belt secured to a mechanism that allows the pad or belt to move in a reciprocating manner, i.e. in both forward and reverse directions, at high speeds. The constant bi-directional movement of the polishing pad or belt as it polishes the wafer provides superior planarity and uniformity across the wafer surface. When a fresh portion of the pad is required, the pad is moved through a drive system containing rollers, such that the rollers only touch a back portion of the pad, thereby eliminating sources of friction other than the wafer that is being polished, and maximizing the lifetime of the polishing pad.